1. Field of the Invention
The present invention relates generally to apparatus and methods for electrically testing printed circuit boards and the like, and more particularly relates to probe structures used in such testing.
2. Description of Related Art
The electrical testing of printed circuit boards and the like is conventionally carried out using a spaced series of spring-loaded, electrically conductive metal test pins, typically referred to as "pogo" pins, which project transversely from a supporting probe plate structure. The test pins are spaced on the probe plate in an array having a relative spacing identical to that of a corresponding spaced array of electrically conductive test points on a side surface of the circuit board to be tested. These test points may be surface mounted pads, vias, plated through-holes, or various combinations thereof.
Each of the resilient test pins typically comprises an outer barrel portion in which an inner contact pin portion is telescoped and outwardly biased toward an extended stop position by a cylindrical spring captively retained in the barrel. To operatively support the test pins, an appropriately spaced series of small circular holes are formed through the probe plate member, and inner end portions of the barrels are suitably secured in the plate openings so that the resiliently deflectable contact pin portions project outwardly from the plate in a "bed of nails" configuration.
The inner barrel ends are conductively connected in a suitable manner to test and analysis circuitry used to receive and evaluate electrical signals received from the test contact points on the printed circuit board via the conductive test pin structures. In testing the printed circuit board, the probe plate is positioned in a spaced apart, facing parallel relationship with the circuit board, with the test pins extending toward the circuit board test contact points in an aligned, outwardly spaced relationship therewith. The probe plate is then moved toward the printed circuit board (or vice versa) until the outer test pin ends engage and are longitudinally depressed by their associated test contact points. Electrical test signals are then appropriately transmitted from the test contact points to the test and analysis circuitry via the electrically conductive test pins.
While pogo pins supported in this manner have long been used in the electrical testing of printed circuit boards, they are subject to a variety of well known problems, limitations and disadvantages. For example, the construction of test pin/probe plate assemblies is a time-consuming and expensive task which must be carried out with great care and precision to obtain the requisite degree of alignment accuracy between each test pin and its associated circuit board test contact point.
Additionally, as the test contact point-to-point spacing or "pitch" in modern high density printed circuit boards continues to decrease as board miniaturization evolves, the accurate use of conventional pogo pin test probing becomes increasingly difficult. Moreover, particularly in the case of high density printed circuit boards, conventional pogo pins tend to damage the board's test contact points. For example, as a practical matter it is not feasible to utilize pogo pins where the test contact point pitch is 15 mils or less without damaging the rather delicate test contact points. However, many modern printed circuit boards now utilize a pitch of 6 mils or less.
It can readily be seen from the foregoing that a need exists for an improved printed circuit board test probe structure and associated probe methods that eliminate or minimize the above-mentioned problems, limitations and disadvantages associated with conventional pogo pin probe structures of the general type described above. It is accordingly an object of the present invention to provide such improved apparatus and methods.